I. Field
The following description relates generally to communication systems and more particularly to a flexible interleaving scheme to enable frequency diversity and to randomize interference.
II. Background
Wireless communication systems are widely deployed to provide various types of communication and to communicate information regardless of where a user is located (e.g., inside or outside a structure) and whether a user is stationary or moving (e.g., in a vehicle, walking). For example, voice, data, video and so forth can be provided through wireless communication systems. A typical wireless communication system, or network, can by multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). A system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), 3GPP Long Term Evolution (LTE), and others.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations through transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link can be established through a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
Various interleaving schemes (e.g., arrangement of data) have poor autocorrelation (e.g., finding repeating patterns) properties. This can be due to inherent repeating differential patterns found in these interleaving schemes. Differential patterns refers to the fact that there can be found pairs of sets of n consecutive sequence indexes where the locations of the elements are related by a linear offset, both before and after the interleaving. However, the two offsets do not need to be the same.
Some communication systems utilize a two-stage interleaving scheme. In this type of scheme, control channel elements are mapped across symbols and then an independent interleaving is performed in each symbol. However, these two-stage interleaving schemes do not provide adequate frequency diversity within the symbols or across the symbols.